1. Field
The present disclosure relates to a stepping motor. More particularly, the present disclosure relates to a stepping motor and a stepping motor system that can detect a step-out phenomenon by using a sensor disposed inside a housing.
2. Related Art
Stepping motors have widely been used in various fields due to their simple structures and ease of control.
In the case of a camera, a stepping motor is often used as an auto focus actuator.
Such stepping motor is generally composed of a rotor that is a permanent magnet attached to a rotation shaft and rotates, and a stator that is an electromagnet fixed to the outside of the rotor. When a pulse current flows through a coil wound around the stator, a magnetic force is generated based on Fleming's left hand rule, and the polarity of the stator is repeatedly changed so that the rotor is turned by an attraction force between N and S poles acting between the rotor and the stator.
The stepping motor does not need a feedback control so that control of the stepping motor is simple. However, the stepping motor is weak to the inertial load and, when the stepping motor is driven at high load and high speed, a step-out phenomenon may occur. Accordingly, stepping motors to which a sensor portion is added to detect the step-out phenomenon when the stepping motor is driven have been developed. For example, if an optical encoder or a magnetic encoder is provided on the outside of the stepping motor, the step-out phenomenon of the stepping motor may be detected by a change in an output signal of the encoder.
However, there is a problem that, when an optical encoder or a magnetic encoder is attached to the stepping motor, a total size of the stepping motor becomes large due to the size of the optical encoder or the magnetic encoder attached to the outside of the stepping motor. In this case, the size of a device using the stepping motor, for example, a camera, is also increased. Furthermore, there is a problem that the cost of the stepping motor is increased due to the price of the optical encoder or the magnetic encoder.